This invention is an improvement in the invention disclosed in U.S. Pat. No. 3,403,520 which relates to a method for setting a utility pole or the like in the ground using foamed plastic instead of back filled dirt for filling the hole; and U.S. Pat. No. 3,564,859 which describes a related method for resetting a pole with foamed plastic. The entire disclosures of U.S. Pat. Nos. 3,403,520 and 3,564,859 are incorporated herein by reference.
Briefly, U.S. Pat. No. 3,403,520 discloses a method for the installation of a pole in the earth by forming a hole in the earth which is only slightly larger than the diameter of the pole where there is insufficient room for tamping tools by inserting the pole into the hole and partly filling the hole with a foamable plastic composition which is permitted to foam filling the void between the pole and the walls of the hole. Preferably, the hole is made by a device which forms a hole without soil removal. Such a device is described in U.S. Pat. No. 3,344,871 in which the hole is found by an apparatus which displaces the soil laterally and compacts the soil in the walls of the hole. U.S. Pat. No. 3,564,859 utilizes the same method of foam filling the voids resulting when an existing installed pole which has become canted or tilted.
One of the foamed plastics contemplated in these patents is polyurethane which is formed and foamed in-situ by reaction of a polyisocyanate and a resin containing active hydrogen atoms and reactive with polyisocyanate. Polyurethane resins are very well suited for use in this application but serious deficiencies are encountered when the hole to be filled with polyurethane foam contains gorund water or runoff water. In such cases, frequently encountered in many parts of the country, foam formation is not satisfactory because spongy foams having a density and strength characteristics which are too low for the purpose result from the reaction of polyisocyanate component with water.
While the source of the problem of unsatisfactory polyurethane foam formation in the presence of large amounts of water is readily apparent to those familiar with polyurethane chemistry a satisfactory solution to the problem is not evident. It is well recognized that water can be used as a foaming agent for polyurethane foams. However, the amount of water used is precisely controlled to give the amount of foaming and foam density required. The reactions involved are as follows, where OCN--P--NCO is a polyisocyanate (containing an organic radical --P-- and HO--R--OH is a low molecular weight and liquid resinous material containing a long chain organic radical --R-- (polyester radical chain, for example) and having groups containing active hydrogen atoms such as the OH-- groups depicted. ##EQU1##
From the foregoing simplified representations, it can be seen that the polyisocyanate (OCN--P--NCO) serves two functions; first as a resin reactant to link two or more molecules of resin (OH--R--OH) to form a larger molecule of solid resin (represented in the bracketed portion); and second, to react with polyisocyanate to form the gas CO.sub.2 which serves as the blowing agent causing foam formation. Since the polyisocyanate is reactive with both water and the resin it is clear that the relative proportions of polyisocyanate, water and resin determine the density and other physical characteristics of the foamed resin. In those applications where a small and predictable amount of water is expected, those skilled in the art can make appropriate reduction in the amount of water added for foam formation, increase in the proportion of polyisocyanate, or both. In this connection, it should be noted that polyisocyanate reacts with water to form a polyamine (H.sub.2 N--P--NH.sub.2) which itself can react with further polyisocyanate to lengthen the resinous chain. Of course, this amine and the resin HO--R--OH may both combine with polyisocyanate to form a larger resinous molecule containing both types or repeating units shown above.
As indicated above, it is possible to make appropriate adjustments in proportions if the amount of residual water can be predicted and if it is small. However, where the amount of water is likely to be large, quite unpredictable or even non-existent, as occurs in the post hole filling application of this invention, no method involving adjustment of proportions can be satisfactorily used to solve the problems associated forming polyurethane foams in the presence of ground water. It is evident that increasing the amount of polyisocyanate is undesirable from an economic standpoint since polyisocyanate is typically the most costly component of a polyurethane foam formulation. Of course, it is also not possible to pump water out of a post hole to be filled with resin since the water quickly returns and in any case remains in deleterious amounts on the surfaces. Moreover, in many areas, water may be present permanently just a few feet below the ground. One solution to the problem which has not been entirely satisfactory, is to set the pole in the ground inside a plastic bag which excludes water and to inject the foam inside the bag which is large enough in diameter to expand to fill the hole upon foam formation. However, the use of bags is cumbersome, the bags, often tear and bags of the dimensions and strength characteristics required are rather costly.